Tutorial: empaqueta una aplicación como plantilla de imagen

"use strict";

const http = require("node:http");
const fs = require("node:fs");
const path = require("node:path");

const port = Number(process.env.PORT || 3000);
const greeting = process.env.GREETING || "Hello";
const dataDir = process.env.DATA_DIR || "/app/data";
const counterFile = path.join(dataDir, "visits.txt");

fs.mkdirSync(dataDir, { recursive: true });

function nextVisit() {
  let visits = 0;
  try {
    visits = Number(fs.readFileSync(counterFile, "utf8")) || 0;
  } catch {}
  visits += 1;
  fs.writeFileSync(counterFile, String(visits));
  return visits;
}

http
  .createServer((req, res) => {
    if (req.url === "/healthz") {
      res.writeHead(200, { "content-type": "text/plain" });
      return res.end("ok");
    }
    res.writeHead(200, { "content-type": "text/plain; charset=utf-8" });
    res.end(`${greeting}! Visit number ${nextVisit()}.\n`);
  })
  .listen(port, "0.0.0.0", () => console.log(`Listening on ${port}`));

FROM node:22-alpine
WORKDIR /srv
COPY server.js .
EXPOSE 3000
CMD ["node", "server.js"]

id: hello-counter
version: 1.0.0
name:
  pt-br: Contador de visitas
  en: Visit counter
description:
  pt-br: Página simples que conta as visitas em disco. Exemplo de template de imagem.
  en: A simple page that counts visits on disk. An image template example.
category: starters
tags: [starter, counter]

inputs:
  - id: greeting
    type: text
    label:
      pt-br: Saudação da página
      en: Page greeting
    default: Hello
    validation: { max_length: 40 }

services:
  app:
    source: { type: image, image: 3f2b8c1e-5d4a-4e6b-9a7c-1b2d3e4f5a6b }
    port: 3000
    ram: { min: 512, recommended: 512 }
    web: required
    env:
      GREETING: "{{inputs.greeting}}"
      DATA_DIR: /app/data
    healthcheck: { path: /healthz, timeout: 60 }
    deploy:
      zero_downtime: { default: "off", locked: true }
      auto_rollback: { default: true }
      rollback: { with_data: optional }

permissions:
  ram: { change: true, below_min: false, above_max: true }

outputs:
  - label:
      pt-br: Endereço
      en: Address
    value: "{{app.url}}"
  - label:
      pt-br: Próximo passo
      en: Next step
    value:
      pt-br: "Abra o endereço e recarregue a página: o contador sobe e sobrevive a reinícios."
      en: "Open the address and reload the page: the counter goes up and survives restarts."